Don't force everybody to call setup_ident().

Don't force everybody to call setup_ident().

Back when only handful commands that created commit and tag were
the only users of committer identity information, it made sense
to explicitly call setup_ident() to pre-fill the default value
from the gecos information.  But it is much simpler for programs
to make the call automatic when get_ident() is called these days,
since many more programs want to use the information when updating
the reflog.

Signed-off-by: Junio C Hamano <junkio@cox.net>